This invention relates to precision machining or micromachining of miniature parts. More particularly, the invention relates to a method and apparatus for holding a miniature part in an exactly replicatable position on a tooling machine such as a lathe, polisher or jig bore.
Miniaturization of parts is a recognized need in today""s increasingly complex and highly technical world. There is a need for developing efficient ways to machine very small components to precise specifications with greater accuracy within closer tolerances. Yet in conventional machine shops, the means for securing miniature parts to commercially available tooling machines are limited or nonexistent. Although small collets, chucks, mandrels and face plates work well for turning diameters or threading thin rods in conventional tooling machines, when specifications require multiple machining operations on the same millimeter-sized part, particularly a complex part, with close tolerances, even collets, chucks, mandrels and face plates are inadequate. Securing and positioning extremely small parts on a tooling machine such as a lathe, polisher or jig bore for precise machining is very difficult and sometimes impossible to do accurately. This difficulty is greatly increased when the miniature part specification requires extremely small tolerances and must be machined on more than one surface or from more than one position with relation to the tooling machine.
In conventional practice, miniature blank parts (i.e., parts without pattern or design, those which have not yet been machined) are first secured to the tooling machine with a collet (which is a split, cone-shaped sleeve) for the initial machining process, then have to be glued (e.g., epoxied) to a mandrel or substrate and accurately aligned with a microscope for any additional machining processes. This multistep process is inefficient, time consuming and often produces inaccuracies. Even when a collet is used for each of more than one machining step, the accuracy of the alignment of the part is compromised each time the part has to be repositioned on the tooling machine. Use of a collet for a multistep machining process requires removal, reversal, coordinate repositioning and precise reattachment of the part blank to the spindle center line of the tooling machine.
When the part is glued to a mandrel or substrate for additional machining steps, realignment of the glued part is often very difficult and depends upon the condition of the equipment and the skill of the operator in repositioning the part on the tooling machine. Removing the glued part after machining or in between steps is often difficult.
In conventional practice, the amount of glue applied, the determination of the position of the part relative to the tooling machine, and the necessary repositioning of the part for additional machining may cause processing difficulties or tolerance inaccuracies resulting in scrap parts.
Although traditionally vacuum forces are used to retain larger parts within tooling machines, such forces are too weak to retain miniature parts in the tooling machine when the tooling machine applies molding or cutting force. So use of vacuums to hold miniature parts, and particularly miniature parts which have to be repositioned more than once for machining more than one surface, is not a satisfactory solution.
Typically, the greatest source of errors in machining with conventional part holders is in relocating a part for subsequent fabrication steps such as additional machining on another surface of the part. During additional fabrication steps, the accuracy of the machining is highly dependant upon the skill, experience and finesse of the operator and even with special effort an operator can usually only achieve accuracy within about 25 micrometers at best. The present invention, in contrast, improves the art by allowing a locator holding the part to be reattached to a kinematic mount on a tooling machine with a significantly greater positioning accuracy (generally about 0.25 micrometer or less). Furthermore, with the invention the alignment of the part for subsequent machining steps does not require a skilled operator and can be accomplished robotically.
Accordingly, it is an object of the present invention to provide a device which enables precision machining of very small or complex miniature parts which is adapted to work with conventional tooling machines.
It is a further object of the present invention to provide a device which can be secured to a tooling machine to hold a part in order to enable an operator to achieve precision machining with accuracy within tolerances of less than about 0.25 micrometer.
It is also an object of the present invention to provide a miniature part holding device which can be secured to a tooling machine for a single machining process and which can be removed and inserted into another tooling machine (or reinserted into the same tooling machine) to allow additional machining on other surfaces of the miniature part without relocating the part from the device between machining processes.
It is another object of the present invention to provide a device which enables milling precise patterns within close tolerances of the specifications, such as required for optics or semiconductor technology, on several surfaces of a miniature part precisely and without any need to handle any surface of the part.
It is yet another object of the present invention to eliminate cost and time of tool realignment and multiple machine setups when a miniature part requires machining on more than one surface of the part.
It is still a further object of the present invention to provide an apparatus to hold two or more separate miniature parts in precise positions during assembly steps.
A final object of the present invention is to provide an apparatus to hold a blank from which multiple parts are machined with selective and precise access to the parts by the machine tool.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, there has been invented an apparatus comprising: at least one locator disposed upon a kinematic mount which can be positioned on a conventional tooling machine and a part support disposed upon the locator. In operation, a blank part to be machined is secured between the part support and the locator. The locator has disposed therein a plurality of steel balls placed at equidistant positions around the planar surface of the locator. The kinematic mount has a plurality of magnets which alternate wth grooves about the circular planar surface of the kinematic mount. The steel balls on the locator are in register with the grooves on the kinematic mount when the locator is placed on the kinematic mount. When the locator holding the part blank is coupled to the kinematic mount, the part is exposed for the selected machining process by holes appropriately positioned in the locator. Because the locator is removably attachable to the kinematic mount by virtue of its shape and the magnetic fields of the magnets in the kinematic mount, it can easily be removed from the kinematic mount, reversed, and repositioned on the kinematic mount for additional machining of the part therein. Further, the locator can likewise be removed from the kinematic mount and placed onto another tooling machine having a properly aligned kinematic mount without losing the position of the part relative to the position of the machine tool because of the part being held securely in the locator during the transition.
A further embodiment utilizes multiple locators in accordance with the invention, with the locators being designed to be stackable, each one adjacent to another, as well as to be removably attachable to the kinematic mount either individually or as a coupled unit. This multiple locator embodiment is particularly useful for micromachining assembly processes or complex processes which involve both micromachining steps and assembly steps with multiple parts. Because of the unique design and use of magnetic forces of all embodiments of the present invention, positioning errors of less than 0.25 micrometer for each machining process can be achieved using the invention devices.